1. Field of the Invention
The present invention relates to an image processor, image processing method and image processing program for drawing on a two-dimensional plane such linear objects as hair, the grass of a turf, and fur, disposed on a virtual three-dimensional space.
2. Description of the Related Art
Currently computer graphics (hereafter CG) for performing image processing by a computer is widely being used for CAD (Computer Aided Design) and CAM (Computer Aided Manufacturing) in science, engineering, manufacturing, gaming and other fields. There are many objects drawn by CG technology, but a certain difficulty has been recognized for writing linear objects such as the fur of mammals, human hair, and rice, wheat and the turf of a landscape.
This is because the shapes of skin and ground, on which linear objects are positioned, are complicated, and how a linear object extends itself (its length and how it extends upward) has no regularity. So in prior arts, methods for drawing such linear objects have been proposed.
According to “Rendering Fur with Three Dimensional Textures” by Kajiya and two others, SIGGRAPH '89, Conference Proceedings, a hair is regarded as a micro-cylinder, and the sum of the diffused light and the reflected light on this micro-cylinder is added as a parameter for rendering (converting information on an object or graphic provided as numeric data to images by calculation), so as to represent the texture of the fur of an animal. This micro-cylinder is an example of an object having anisotropic reflection characteristics, and is introduced as a “texel” in “Rendering Fur with Three Dimensional Textures” by Kajiya and two others, SIGGRAPH '89, Conference Proceedings.
While the reflections of light are the same in all direction in “Rendering Fur with Three Dimensional Textures” by Kajiya and two others, SIGGRAPH '89, Conference Proceedings, according to “Mounting by vertex shader of pseudo fur lighting” by Imakiire, XFC 2001 [Searched on Aug. 25, 2002] Internet <URL: http://if.dynsitc.net/t-pot/program/23_fur/index.html> the representation of fur by Goldman, where the reflection components and the transmission components are separated, is advanced one more step and a fur representation, unique to the author of “Mounting by vertex shader of pseudo fur lighting” is introduced to shading. According to “Real-time Fur Over Arbitrary Surfaces” by Jerome Lengyel and three others, ACM Symposium on Interactive 3D Graphics 2001, pp. 227-332 [Searched on Aug. 25, 2002] Internet <URL: http://research.microsoft.com/˜hoppe/fur.pdf>, a hair, which vertically extends from skin, is cut by a plurality of semi-transparent layers perpendicular to the height direction, and semi-transparent layers are drawn a plurality of times from the one closer to the skin and are layered so as to draw a hair at high-speed. In “Real-time Fur Over Arbitrary Surfaces”, this semi-transparent layer is introduced as a “shell”.
According to Japanese Patent Application Laid-Open NO. 2004-54612, instead of slicing fur in the height direction and regarding each slice as a map corresponding to a different shell, as stated in “Real-time Fur Over Arbitrary Surfaces” an image processor, which projects an entire hair on a two-dimensional map which corresponds to the skin surface, so as to enable high image quality representation with small memory capacity, is proposed.